Stray-limiting device



H. L. HOYT, JR. ET AL 1,754,557

STRAY LIMITiNG DEVICE April 15, 1930.

2 Sheets-Sheet 1 Filed Oct. 16, 1926 April 15, 1930. H. HOYT, JR, ET AL 1,754,557

' STRAY LIMITING DEVICE Filed Oct, 16, 1926 2 Sheets-Sheet 2 P/afe Gar/em- NVENTORS ATTORNEY Patented Apr. 15, 1930 UNITED STATES PATENT OFFICE HAZEN L. HOYT, JR., AND BOWDEN WASHING-TON, OF NEW YORK; N. Y.

STRAY-LIMITING DEVICE Application filed October 16, 1926. Serial No. 141,982.

The main object of our invention is to limit the pernicious effects in radio reception of atmospheric disturbances of an intense but largely aperiodic nature commonly known as strays, atmospherics, static and the like.

Another object is to prevent the shock excitation, and consequent production of comparatively long damped trains of oscillations in the resonant circuits of a radio receiver, caused by the extremely high intensity of static impulses by limiting this intensity to substantially that of the desired signal.

Referring to the drawings:

Figure 1 is a schematic wiring diagram of one embodiment of our invention.

Figure 2 is a graphic representation of the relation between input voltage and output current of a vacuum tube under certain conditions.

Figure 3 shows the residual signal current after the application of our device.

Figure 4 suggests the residual of the cur rent produced by strays in the output of our device.

In Figure 1 the antennalO is connected through the high resistance 11 to the ground 12 so as to form an aperiodic circuit. The grid 13 of the vacuum tube 14E is connected to the upper or high end of the resistance 11. The lower end of this resistance is connected to variable contact 15 of the voltagedivider 16 which is connected to the terminals of the biasing battery 17 the negative terminal of which is connected to the filament 18 of the tube 14.

The plate 19 of this tube is supplied with unidirectional voltage from the anode bat tery line 20 through the choke 21. One terminal of the condenser 22 is connected to the plate 19 and the other terminal is connected through the inductance 23 to the plate 2st of some form of two electrode rectifier tube 25. The filament 26 of this tube is connected to the common filament supply lines 27 and 28.

The inductance 23 is coupled to the inductance 29 which forms a part of the tuned grid circuit of the first stage of tuned radio frequency amplification 30, a secondstage of tuned radio frequency amplification is-shown at 31 anda tuned detector stage at 32. An indicating device such as the telephone receiver 34, is connected wit-l the outputof the detector tube 33;. or an audio frequency amplifier may be inserted between the detector output and the indicating device.

In Fig. 2 the curve lO delineates the plate current grid volta e characteristic of the vacuum tube 1 1- (Fig. 1). The voltage divider 16 should be adjusted so as to bring the no-signal plate current almost to saturation as at 11. The signal voltage as at 42 applied to the grid will. tend to produce a plate current such as 43 while the stray voltage a4 applied to the grid Will tend to produce a plate current such as 45. However, on account of the rectifier (Fig. 1) the current produced by the signal voltage through the inductance 23 will be substantially of the form shown in Figure 3 while the stray volt age may produce current pulses of the general nature of those shown in Figure 1.

Current pulses such as are shown in Fig. 3 being periodic and of proper duration will efficiently excite the tuned grid circuit of the tube (Fig. 1) while irregular pulses such as those shown in Figure t will not excite this circuit to any great extent as they will be of no particular period and their amplitude will be no greater than that of the signal, so that any great amount of shock excitation cannot occur.

It should be understood that the combination disclosed of a three electrode tube operating near a bend in its characteristics and a rectifier in the output circuit of this tube may be used other than as the first radio frequency amplifier. Such a combination may be used, for instance, as the last stage of audio frequency amplification as a stray limiting device.

e claim 1. In a stray limiting circuit for radio reception, a three electrode vacuum tube, means for operating the tube near the upper bend of the grid-voltage, plate-current characteristic curve, an aperiodic inputcircuit for said tube, an output circuit for said tube containing a condenser, a rectifier and the primary of a radio frequency transformer connected in series, a periodic amplifying system connected to the secondary of said transformer, and means including a choke coil for supplying unidirectional voltage to the anode of said vacuum tube.

2. In a radio receiver having collecting means, radio frequency amplifying means and detecting means, stray limiting means coupling said collecting means and said radio frequency amplifying means and consisting of a three electrode vacuum tube having means for adjusting the operating point of the grid of the tube to a predetermined point near one of the bends in the grid-voltage plate current characteristic curve, a two-electrode rectifier tube and a radio frequency transformer, means for connecting the primary of said transformer in series With the anode circuits of said tubes and the secondary thereof in the input of said radio frequency amplifying means.

HAZEN L. HOYT, JR. BOVVDEN lVASHINGTON. 

